1. Field of the Invention
The invention generally relates to a method and apparatus for contacting sheet-like material with a treating medium. More particularly, the invention relates to an improved method and apparatus for the deacidification of cellulose based materials such as books, magazines, newspapers, documents and the like.
2. Description of the Invention Background
The deterioration of paper, books and newspapers is well-known and a recognized threat to permanence of library and archival collections. The severity of the threat is dependent in large part on the type of cellulose and the manufacturing process used to produce the cellulose based material; however, numerous environmental factors, such as air pollution, exposure to natural and artificial light, microbiological attack, and physical handling also play a part in the deterioration. One of the most pervasive forms of deterioration is acidic attack of the cellulose structure by acidic species present in the cellulose material, which can shorten the useful life of paper products from centuries to years. The primary contributors to the presence of acidic species in the cellulose based material are the manufacturing processes used to make the cellulose material and air pollution.
Acidic attack of the cellulose material results in the breakdown of the cellulose structure, rendering the paper embrittled and discolored. Paper produced from wood pulp fiber is particularly susceptible to attack because in most instances the pulp fiber must be treated with various chemicals to produce the paper with the proper opacity and of sufficient quality for use. Many of the chemicals used in producing the paper are either acidic or are deposited by methods employing acids and residual amounts of the acidic species remain in the cellulose matrix of the finished paper product. The acidic attack of the cellulose based materials is exacerbated by air pollution which, in essence, provides a perpetual source of chemicals, such as sulfur, nitrogen and carbon-based oxides, that can be hydrolyzed to form acids. The presence of these chemicals in the air threatens not only to worsen the attack of inherently acidic paper product but will, over time, produce acidic conditions in paper products that were initially alkaline or neutral. The accelerated deterioration resulting from air pollution is a significant long term concern in that many of the library and archival materials are located in urban areas and subject to high levels of industrial pollutants. Thus, prevention of paper deterioration by acidic attack is necessarily a bifurcated problem of neutralizing the acidic conditions that are currently present in the paper and of providing for the neutralization of acidic species that are introduced over time.
A significant amount of research has been devoted to developing chemicals and methods to neutralize the acidic species in cellulose based material and to provide an alkaline buffer so as to militate against the development of acidic conditions over time. A wide variety of processes have been developed using alkaline species to neutralize acidic species involving both liquid and vapor treatment techniques, for example U.S. Pat. No. 3,676,055 (magnesium methoxide and methanol); U.S. Pat. No. 3,676,182 (alkali carbonates and bicarbonates); and U.S. Pat. No. 3,969,549 (volatile metal alkyls). However, the chemicals and techniques of those processes all suffer from a number of drawbacks, such as toxicity, odor, high cost, reactivity with and solubility of various inks and paper, in addition to incomplete treatment of bound material despite the use of liquid immersion techniques.
U.S. Pat. No. 4,522,843 issued Jun. 11, 1985 to Kundrot discloses the use of dispersions of alkaline particles consisting of a basic metal oxide, hydroxide or salt carried by inert gas and liquid carriers, which overcomes many of the drawbacks of the prior art by providing alkaline species that do not form deleterious neutralization reaction products and that can be readily deposited to provide an alkaline reserve and liquid carriers that are inert with respect to a vast majority of inks, dyes and cellulose materials. Preferred embodiments of the Kundrot patent provide for a treating solution consisting of MgO.sub.2 particles dispersed in chlorofluorocarbon (i.e. Freon) carrier. The unavailability of chlorofluorocarbon has rendered the practice of the Kundrot patent commercially unfeasible.
U.S. Pat. No. 5,409,736 issued Apr. 25, 1995 to Leiner et al., hereinafter the "'736 patent", discloses the use of perflourinated carriers and associated surfactants, in lieu of chlorofluorocarbon compounds used in the Kundrot method, as a suitable liquid carrier for the alkaline particles. The treating solution compositions and the methods disclosed by the '736 patent are used in conjunction with the present invention and are incorporated herein by reference.
The Kundrot patent discloses the use of spray nozzles oriented above a single submerged book and to direct a wide deflection spray vertically parallel to the spine of the book. The technique was not overly effective at contacting the area of the sheets near the center of the book, where the material is bound, sometimes referred to herein as the "gutter" of the bound material.
U.S. Pat. No. 5,422,147 issued Jun. 6, 1995 to Leiner et al., hereinafter the "'147 patent" disclosed a method and an apparatus that significantly improved the effectiveness of treating bound material. The inventors found that by causing relative parallel movement between the spine of the material and the treating medium a significant improvement can be achieved in both the extent of treatment per page and in reducing the page to page variation in the treatment. A preferred embodiment of the apparatus described in the '147 patent provides for the immersion of the cellulose materials in a treating medium followed by the production of relative movement between the liquid solvent and the cellulose material in a direction generally parallel to the spine of the material. The relative movement is produced by either movement of the cellulose material, the treating medium or both. Relative parallel movement is believed to assist in separating the sheets of the cellulose material to allow penetration of the treating medium. That movement also allows the treating medium to flow across the spine of bound material, thereby resulting in more complete coverage by the treating medium.
The commercial viability of a mass treatment method for deacidification or any other treatment depends on the ability of the process to fully treat the material in a manner that is both cost effective and timely. While the apparatus and process described in the '147 patent provide superior results in terms of the extent of deacidification and treatment time, the commercial viability and appeal of a mass deacidification procedure requires the development of ever more efficient and effective processes and apparatuses to perform mass treatment of cellulose based material. Accordingly, it is an object of the present invention to provide an improved process and apparatus for the efficient and cost effective deacidification of cellulose based materials.